The present invention relates to a power transmission device in which an output shaft always rotates in the same direction when an input shaft is rotated in either forward or reverse direction.
There is a driving device such as a manual pencil sharpener and various types of drilling machines in which a driving unit at an output side is operated when a handle is rotated in one direction (forward rotation) and the driving unit becomes idle or a non-operating state when the handle is rotated in a reverse direction (reverse rotation). In terms of configuration, a device may be provided with a one-way clutch for transmitting a rotational drive of a handle to a driving unit. In such a driving device, from an operational point of view, the operational efficiency can be improved when a driving unit (output side) can rotate in the same direction regardless of the forward rotation or the reverse rotation of a handle (input shaft side), i.e. a rotational direction of the handle. However, no conventional power transmission mechanism can transmit the drive power in such a manner, and there is no prior art document showing a power transmission device at least with a simple or compact configuration.
Japanese Patent Publication (Kokai) No. 10-331941 has disclosed a conventional one-way clutch. As shown in FIG. 8(a), the one-way clutch includes an outer member 50, an inner member 55, and planetary gears 60. The outer member 50 is a gear having external teeth 51 and internal teeth 52 formed on a peripheral wall. The inner member 55 has a holding portion rotatably disposed in an inside of the outer member 50. The holding portion 56 has several depressions 57 provided on a common circle and having an opening at a side opposite to the internal teeth, and a plurality of projections 58 is provided in an inside of the depressions. Each of the planetary gears 60 engages the internal teeth 52 and loosely housed in each of the depressions 57.
As shown in FIG. 8(b), in this clutch, when the inner member 55 is rotated in one direction relative to the outer member 50, the planetary gear 60 rotates at the inside of the depression 57 accompanied with the rotation of the inner member (rotates idle relative to the outer member 50). As shown in FIG. 8(c), when the inner member 55 is rotated in the opposite direction relative to the outer member 50, the planetary gear 60 rotates in association with the rotation of the inner member, and a part of the teeth of the planetary gear 60 engages the projections 58 so that the outer member 50 rotates together.
As described above, there are only a small number of conventional power transmission devices having a simple and small mechanism, in which an output shaft can always rotate in the same direction when an input shaft is rotated either in the forward rotation or reverse rotation. Therefore, in an application of a driving apparatus, it is difficult to obtain high operational efficiency or easy handling in the case of the manual operation. Also, it is necessary to increase the number of switching between the forward rotation and reverse rotation of the motor more than necessary in the case of the automatic operation.
The present invention has been developed from the above-mentioned background, and an object of the present invention is to provide a power transmission device having a simple and compact mechanism in order to improve the operational efficiency and make it easy to apply.
Further objects and advantages of the invention will be apparent from the following description of the invention.